The steady-state model of the universe suggests the universe always had and will always have the same density. The theory reconciles the apparent evidence that the universe is expanding by suggesting that the universe generates matter at a rate proportionate to the universe's rate of expansion.

The Ekpyrotic model suggests our universe is the result of a collision of two three-dimensional worlds on a hidden fourth dimension. It doesn't conflict with the big bang theory completely, as after a certain amount of time it aligns with the events described in the big bang theory.

The big bounce theory suggests our universe is one of a series of universes that first expand, then contract again. The cycle repeats after several billion years.

Plasma cosmology attempts to describe the universe in terms of the electrodynamic properties of the universe. Plasma is an ionized gas, which means it's a gas with free roaming electrons that can conduct electricity.

The Big Bang Theory - This is the leading theory and scientists have carefully explore the 4 pillars to this theory including: